1. Field of the Invention
The present invention relates to a valve manifold for controlling flow between a main flow line and a pressure sensor and, more specifically, to such a valve manifold that is self-draining.
2. Description of the Prior Art
It is often desirable to determine the flow or pressure of a fluid, e.g., a gas, through a main flow line, e.g., a pipeline. Typically, this can be accomplished by a flow restriction disposed in the main flow line, there being pressure taps on each side of the restriction for obtaining high and low fluid pressures. Such a flow restriction may comprise an orifice plate, a flow nozzle, a venturi tube, etc. The high and low pressures taken from opposed sides of the flow restriction in the main flow line are detected by a pressure sensor/transmitter assembly that measures and transmits the measured pressures or pressure differential by a suitable mechanical or electronic signal or the like to a remote location, e.g., a control room, where the pressure or pressure differential may be monitored and/or recorded by an operator.
A valve manifold is normally mounted between the main flow line and the pressure sensor. The manifold is used to control flow to the pressure sensor while permitting blocking, venting, zero checks, and calibration. The manifold typically includes a plurality of valves, each movable between open and closed positions relative to a flow pathway in the manifold so as to control the flow of fluid through the pathway.
Fluid pressure sensor/transmitters, particularly such sensor/transmitters of the differential pressure type typically employ diaphragms in both the low and high pressure inlets to the pressure sensor to detect the high and low pressures to which they are exposed. As disclosed in U.S. Pat. No. 5,277,224, it is desirable, in order to minimize leak paths, to minimize the interface connections between the pressure sensor and the main flow line. As also taught in U.S. Pat. No. 5,277,224, this can be accomplished, in part, by directly coupling the valve manifold to the pressure sensor. While this reduces leak paths and the space required for the manifold/pressure sensor system, it can pose significant problems.
Pressure sensors of the type under consideration typically employ diaphragms. These diaphragms are extremely fragile, expensive, and difficult to install in the pressure sensor. Further, in cases where the valve manifold and pressure sensor are directly coupled to one another, the diaphragms are closely positioned to the face of the manifold to which the pressure sensor is attached. In these direct coupled manifold/pressure sensor assemblies, one face of the manifold, referred to as the instrument face, sealingly abuts a face of the pressure sensor. The instrument face of the manifold is provided with a low pressure outlet and a high pressure outlet, both of which are relatively shallow, cylindric cavities. The cylindric cavities are in register with low pressure and high pressure inlets, respectively, in the face of the pressure sensor sealingly abutted by the instrument face of the manifold. The diaphragms are positioned in the low pressure and high pressure inlets of the pressure sensor close to the mouths thereof. Accordingly, when the manifold and pressure sensor are mated, the cylindric cavities cooperate with the diaphragms to form generally cylindric chambers of a small cylindrical height relative to the cylindrical diameter.
Although manifold/pressure sensor assemblies of the type under consideration can be mounted in a variety of ways, it is common, when the fluid pressure being measured is a gas, to mount the manifold such that the instrument face is generally horizontal and facing up, the pressure sensor accordingly being mounted above the manifold. It is not uncommon when measuring gas pressures for there to be condensation of liquids in the manifold, which occurs either during or after pressure measurements. Any liquid remaining in the relatively shallow cylindric chambers described above, if not removed, may interfere with subsequent pressure measurements, can cause corrosion of the metal diaphragms, or in certain, adverse climatic conditions, freeze and rupture the diaphragms. Accordingly, it becomes expedient, to the extent possible, that any liquid that collects in the manifold, by whatever mechanism, be removed. In particular, any liquid remaining in the cylindric chambers must be removed to avoid the problems discussed above.
In cases where the manifold is utilized in pressure measurements on a liquid source, the instrument face of the manifold is generally likewise disposed in a horizontal plane but is facing downward rather than upward as in the case with gas measurements, the pressure sensor/transmitter being mounted below the manifold. In measuring liquid pressures, it is important, for accuracy of measurement, that the liquid in the cylindric chambers be free of gas bubbles, which could collect on the diaphragm surface, giving a false reading. Accordingly, it is clearly desirable for the manifold to be designed such that any gas bubbles in the cylindric chambers be provided with escape pathways that slope upward from the instrument face of the manifold so that any gas bubbles in the liquid can rise out of the cylindric chambers, away from the diaphragm faces.
It is common in prior art manifold design, in order to form the relatively complex passageway system, to utilize xe2x80x9cconstruction holes,xe2x80x9d which are simply bores in the manifold body that allow passageways to be drilled and interconnected with other passageways. These construction holes, even though they are plugged, are a potential source of leakage. Alternately, they frequently provide dead spaces within the manifold body where liquid and gas bubbles can collect. Thus, elimination of the construction holes eliminates one possible source of leakage and liquid collection or pooling in the manifold body.
It is therefore an object of the present invention to provide an improved valve manifold.
Another object of the present invention is to provide a valve manifold for use with pressure sensors of the differential pressure type.
Still a further object of the present invention is to provide a self-draining valve manifold.
Another object of the present invention is to provide a wafer-type valve manifold that eliminates the need for construction holes or other such bores to accommodate drilling of and interconnection of internal passageways.
The above and other objects of the present invention will be apparent from the drawings, the description, and the appended claims.
The valve manifold of the present invention is adapted to be positioned between a main flow line and a pressure sensor to control fluid flow from the main flow line to the pressure sensor. The manifold has a body with a first face, an opposed, substantially planar second face, and a peripheral wall. A high pressure inlet, a low pressure inlet, a high pressure drain port, and a low pressure drain port are formed in the first face, while a high pressure outlet and a low pressure outlet are formed in the second face. An equalizer valve cavity is formed in the peripheral wall and is provided with an equalizer valve that controls fluid communication between the high pressure outlet and the low pressure outlet. A high pressure block valve cavity is also formed in the peripheral wall, the high pressure block valve cavity, the high pressure inlet, and the high pressure valve being interconnected, a high pressure block valve being disposed in the high pressure block valve cavity to control fluid communication between the high pressure inlet and the high pressure outlet. A high pressure vent valve cavity is formed in a first, substantially planar, side surface of the peripheral wall, the first, side surface being at an acute angle relative to the second face of the manifold body. A straight, high pressure vent passageway connects the high pressure vent valve cavity and the high pressure outlet, the high pressure vent passageway sloping in a direction away from the second face and being substantially normal to the first side surface. The high pressure vent valve cavity and the high pressure drain port are connected, flow therebetween being controlled by a high pressure vent valve disposed in the high pressure vent valve cavity. In like manner to the high pressure arrangement discussed above, the manifold further includes a low pressure block valve cavity formed in the peripheral wall, the low pressure block valve cavity, the low pressure inlet, and the low pressure outlet being interconnected, a low pressure block valve being disposed in the low pressure block valve cavity to control fluid communication between the two pressure inlet and the low pressure outlet. Likewise, a low pressure vent valve cavity is formed in a second, substantially planar side surface of the peripheral wall, the second side surface also being at an acute angle relative to the second face of the manifold body. A straight, low pressure vent passageway connects the low pressure vent valve cavity and the low pressure outlet, the low pressure vent passageway sloping in a direction away from the second face and being substantially normal to the second side surface. The low pressure vent valve cavity and the low pressure drain port are connected, flow therebetween being controlled by a low pressure vent valve disposed in the low pressure vent valve cavity.